[v2.6.34-stable 41/77] genirq: Fix race condition when stopping the irq thread

[Paul Gortmaker]

From: Ido Yariv <ido@xxxxxxxxxx>

                   -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git
    If you see a problem with using this for longterm, please comment.
                   -------------------

commit 550acb19269d65f32e9ac4ddb26c2b2070e37f1c upstream.

In irq_wait_for_interrupt(), the should_stop member is verified before
setting the task's state to TASK_INTERRUPTIBLE and calling schedule().
In case kthread_stop sets should_stop and wakes up the process after
should_stop is checked by the irq thread but before the task's state
is changed, the irq thread might never exit:

kthread_stop                    irq_wait_for_interrupt
------------                    ----------------------

                                 ...
...                              while (!kthread_should_stop()) {
kthread->should_stop = 1;
wake_up_process(k);
wait_for_completion(&kthread->exited);
...
                                     set_current_state(TASK_INTERRUPTIBLE);

                                     ...

                                     schedule();
                                 }

Fix this by checking if the thread should stop after modifying the
task's state.

[ tglx: Simplified it a bit ]

Signed-off-by: Ido Yariv <ido@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/1322740508-22640-1-git-send-email-ido@xxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
---
 kernel/irq/manage.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 9080985..8668523 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -479,8 +479,9 @@ static irqreturn_t irq_nested_primary_handler(int irq, void *dev_id)
 
 static int irq_wait_for_interrupt(struct irqaction *action)
 {
+	set_current_state(TASK_INTERRUPTIBLE);
+
 	while (!kthread_should_stop()) {
-		set_current_state(TASK_INTERRUPTIBLE);
 
 		if (test_and_clear_bit(IRQTF_RUNTHREAD,
 				       &action->thread_flags)) {
@@ -488,7 +489,9 @@ static int irq_wait_for_interrupt(struct irqaction *action)
 			return 0;
 		}
 		schedule();
+		set_current_state(TASK_INTERRUPTIBLE);
 	}
+	__set_current_state(TASK_RUNNING);
 	return -1;
 }
 
-- 
1.7.12.1

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